The invention relates broadly to a method for testing resilience of solid particles. A specific application of the invention is to provide a method for checking resilience of solid particles which are to be coated in a fluidized bed operation.
There are various chemical compositions in which the product is marketed in the form of solid particles, such as pellets or granules. In many of these formulations, such as medicinal preparations for humans or animals, the active ingredient will be contained in a base particle along with other substances such as extenders and fillers. Some of these preparations require that the base particle be coated with a material which will keep the active ingredient from dissolving in body fluids until the medicament reaches a desired point of release in the body.
A technique which is frequently used for coating the base particles is referred to as a spouting fluidized bed coating operation. In general, this technique involves placing the base particles in a hollow chamber which includes an eductor tube positioned inside the chamber. A drying gas and coating fluid are directed into the chamber through the eductor tube at a velocity which causes the particles to fluidize in the chamber. In the fluidized condition the particles will continuously recycle from the chamber upwardly through the eductor tube. This technique gets its name from the fact that during the coating operation the particles being propelled above the eductor tube resemble a spouting fluid.
For those preparations in which the base particle is to be coated in a spouting fluidized bed operation, the resilience of the particle is a significant factor to be considered. For example, during the coating operation, the particles in the coating chamber are subject to a high degree of abrasion. In this situation, if the particles have a low resilience characteristic, many of them will rupture and deform during the coating operation. The result is a substantial amount of dust particles and other particles which do not have a desirable size, and which may also have an irregular shape. It is difficult to apply a uniform coating to such particles, particularly those having an irregular shape.
Because of the situation described above, it is desirable to determine the resilience of the base particles of a formulation prior to coating the particles. One of the prior testing procedures involves placing a representative sample of the uncoated base particles on the screen of a mechanical shaker device. The uncoated particles placed on the screen are of a size suitable for coating, and the openings in the screen are usually several sizes smaller. The screen is shaken for several minutes and those particles which fall through the openings comprise the dust phase, which is unsuitable for coating. The screening test for particle resilience is not a reliable procedure. The reason for this is that the screen test does not simulate the conditions which occur when particles are coated in a fluidized bed operation.